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Poult Sci 2007. 86:1850-1855
© 2007 Poultry Science Association
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ENVIRONMENT, WELL-BEING, AND BEHAVIOR

Motor Incoordination, Intracranial Fat Bodies, and Breeding Strategy in Crested Ducks (Anas platyrhynchos f.d.)

J. Cnotka1, H. D. Frahm, A. Mpotsaris and G. Rehkämper

C. and O. Vogt Institute of Brain Research (Behaviour and Brain), University of Düsseldorf, Universitätsstr. 1, D-40225 Düsseldorf, Germany, and Scientific Poultry Yard of the German Association of Poultry Breeders, D-41569 Rommerskirchen, Germany

1 Corresponding author: cnotkaj{at}uni-duesseldorf.de


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Some Crested ducks (CR) are burdened with an intracranial fat body that, depending on the size and location, may lead to varying degrees of motor incoordination. A behavioral test is proposed that helps to identify those CR individuals bearing the problematical fat body. The test consists of putting the ducks on their backs and measuring the time required to right themselves. This was repeated 13 times per animal, and means were calculated. The minimum time required was 0.5 s, and the maximum was 62.6 s. Individuals that show motor incoordination need more time than ducks without such problems (14.3 s in contrast to 1.2 s) and exhibit a larger intracranial fat body. Ducks used for breeding should require no more than approximately 1 to 2 s to right themselves. In an allometric comparison with 3 other domestic duck breeds, CR show a significantly smaller brain; specifically, the cerebellum, tegmentum, apicale hyperpallium, and olfactory bulb are reduced. The relationship between fat body and these structures was discussed.

Key Words: Crested duck • motor incoordination • intracranial fat body • righting test • breeding management


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
In a previous paper it was reported that the brains of Crested ducks (CR, Figure 1Go) show some peculiarities, such as reduced olfactory structures and relatively small cerebella (Frahm et al., 2001). Additionally, many individuals bear a fat body inside the skull that could vary in size and position (Figure 2Go). Depending on its size and probably its position in relation to the brain, the fat body has a negative impact on behavior (Cnotka et al., 2006). Often motor coordination is poor as demonstrated by a tottering walk, and some animals are even unable to right themselves after having fallen on their back. Apparently this condition is independently from age or sex (Frahm et al., 2001; Cnotka et al., 2006). In CR that are bred for exhibition, this deficit has caused a regional government in Germany to ban the breed and to forbid breeding them. It has been reported that such poor motor coordination is also occasionally present in other meat breed duck populations (Kamar et al., 1983). Thus, the problem might also be economically relevant.


Figure 1
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  		Figure 1. Heads of Crested ducks.

 

Figure 2
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  		Figure 2. Dorsal view of a brain with incorporated fat body (*) of middle size, which is positioned within the tentorium cerebelli.

 
It is believed that, in the case of CR, a severe breeding problem exists that should be solved by good management rather than by eliminating a breed completely. The first step in coming to grips with this problem is to analyze it carefully and to develop a breeding strategy that allows a breeder to eliminate this detrimental trait from their breeding populations, assuming that it is heritable (Lancaster, 1990). The breeders need a simple tool to identify and eliminate individual carriers of the undesirable defect even if it is not obvious and behavior in daily life looks quite normal. Though discussed in some papers (Krautwald, 1910; Brinkmeier, 1999), the existence of a crest and its size is not a reliable predictor of the fat body (Bartels et al., 2001; Frahm et al., 2001, 2005). Thus other phenotypic measures must be identified that are associated with this trait.

It is the goal of the present paper to draw attention to behavioral traits that indicate motor coordination deficits. In parallel we have analyzed whether subjects identified as malfunctional do have a more or less prominent fat body inside their skulls.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Behavioral Observations and Test
For checking the motor abilities and to provoke the system of motor coordination 21 adult CR (10 drakes, 11 ducks) coming from our own stock were used in a special test. The idea for this test results from the fact that ducks with serious problems in motor coordination often are unable to right themselves and stand up if they happen to lie on their backs. Among the 21 ducks investigated, 9 individuals showed motor incoordination at least one time in their lives. These ducks featured the symptoms in different manners, such as tottering or tumbling down, including falling on their backs, but appeared quite normal in their daily lives. The deficits became apparent during or just following collection of the ducks for handling. After such treatment, many of them recovered quickly and were inconspicuous again in daily life. The other 12 ducks were completely inconspicuous in their behavior, at least in respect to their motor coordination. So, it was possible to use the following test on 2 distinguishable groups of ducks.

For that, the test animals were put on their backs with the legs upwards (Figure 3Go). Then the time required for them to stand up to both feet was measured. Every individual was tested 13 times over a period of 3 months, and the average time was calculated for that individual.


Figure 3
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  		Figure 3. Behavioral test. A Crested duck was put on its back, and the time required for the animal to right itself was measured.

 
Morphometry of the Brain
The investigation of the brain anatomy was based on 21 CR brains from the tested animals. For comparison 26 brains from 3 other domestic duck breeds called Pommeranian ducks (n = 10, 5 drakes/5 ducks), Abacot Ranger ducks (n = 6, 3 drakes/3 ducks), and Hochbrutflugenten (n = 10, 5 drakes/5 ducks) were used. The Pommeranians (also known in England as Swedish ducks) are ducks with relatively large bodies, originally bred for meat production; the Abacot Ranger ducks are a little bit smaller and more dainty or graceful. They are classified as very robust. The Hochbrutflugenten are relatively small animals, capable of flight and with a tendency to nest on elevated places, e.g., in trees some meters above the ground. All specimens of these breeds were obtained from organized breeders and were at least 1 yr old.

For the brain analysis and allometrical comparison, we determined body size, brain size, total brain volume, volume of the fat body, and the volume of 14 other areas of the brain (hyperpallium apicale, hyperpallium densocellulare, mesopallium, nidopallium, globus pallidus/lateral striatum, septum, hippocampus, area prepiriformis, bulbus olfactorius, tegmentum, cerebellum, tectum, tractus opticus, and diencephalon). For this the animals were killed by an overdose of pentobarbital barbiturate. After weighing they were perfused with physiological saline solution and a fixative (Bodian’s fluid). The brains were carefully dissected, weighted, and embedded in paraffin. The dissection had to be carried out within 3 h after perfusion to receive a substantial and comparable brain weight. After being embedded in paraffin, the brains were cut into 20-µm-thick coronal sections. A defined number of the sections were stained for cell bodies.

For morphometry the contours of the brain and the brain structures were drawn with a digital pen using a camera lucida. Then the resulting values were multiplied by the section thickness, the distance between the sections, and the conversion factor of shrinkage to receive the fresh volume.

The methods for preparation and measurement are described in detail in Frahm and Rehkämper (1998) and Frahm et al. (2001). All measurements and calculations were done using the computer program NucleoScope (Mpotsaris, 2006; Mpotsaris and Rehkämper, 2006).

To compare volumes of brain structures in different breeds with different body sizes, allometric methods were used to rule out the influence of the body size. The relationship between brain volume, brain structure volume, and BW are given by the formula:


Formula

where y represent the brain or brain structure size, b the intercept of the regression line with the abscissa, x the BW, and a the slope of the line. A regression line was calculated for all data points of the CR and the reference breeds Pommeranian, Abacot Ranger, and Hochbrutflugenten.

Statistical Analysis
Differences between the 2 examined groups for average righting time and for fat body volume were calculated and evaluated using the Mann-Whitney Rank Sum Test.

For statistical analysis of the differences in brain structure volumes between the CR and the pooled reference breeds allometric size indices (SI) were calculated. These indices represent numerical measures of the distance of individual data points from the regression line. All points on the line represent a SI of 100, so for example an SI of 200 would mean that a structure has doubled its size from the value predicted from the reference line. A detailed description of this method is given by Stephan et al. (1988). Differences between SI of CR and the reference group were evaluated using Student’s t-test. Additionally correlation analyses between fat body volume and brain size or brain part size were calculated using Pearson product moment correlation.

All research was performed in accordance with the official German regulations for research on animals.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
Behavioral Test
Figure 4Go shows the average times required by the 21 CR individuals to right themselves from an inverted position. Because of their behavior in daily life, the ducks were divided in 2 groups (see above): the 9 individuals with several behavioral deficits (affected CR) and the 12 individuals without any problems (normal CR). The minimum time required was 0.5 s, and the maximum was 62.6 s. On average the affected CR performed poorly. They required 14.3 ± 23.04 s and ranged from 0.9 to 62.6 s. The normal CR performed well, required 1.2 ± 0.70 s and ranged from 0.5 to 2.9 s. The average times of the 2 groups differ significantly (T = 130.5; n = 9, 12; P = 0.028).


Figure 4
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  		Figure 4. Behavioral test. Time required by 21 Crested ducks (CR; 9 affected ducks, 12 normal ducks) to pass the righting test. Vertical bars indicate means with standard errors of the mean (*P = 0.028).

 
Morphometrical Analysis
On average the BW of all affected CR investigated measured 2,312 ± 91.5 g and ranged from 1,885 to 2,740 g. The corresponding data on brain size are 7,304 mm3 ± 425.3 with a range from 5,333 to 9,547 mm3. Normal ducks show an average BW of 2,234 ± 95.8 g (ranged from 1,825 to 2,960 g). The corresponding data on brain size are 6,624 mm3 ± 265.0 with a range from 5,111 to 8,060 mm3. The size and the topography of the intracranial fat bodies were variable. The volumes of the fat bodies of the examined duck population varied from 113 to 3,891 mm3, from 2 to 41%, respectively, of total brain volume. Two examined (normal) ducks did not show a fat body.

However, the 2 groups of the 9 preselected affected CR individuals and 12 normal CR individuals without extraordinary behavior differ significantly in fat body size (Figure 5Go). The latter group shows a significantly smaller fat body (576.7 ± 158.16 mm3) in comparison with the former ducks (1,605.4 ± 401.82 mm3; t-test, t = 2.632, df = 19, P = 0.016).


Figure 5
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  		Figure 5. Fat body volumes of Crested ducks (CR) with poor test results (affected CR, n = 9) in comparison to those with good performance (normal CR, n = 12). Vertical bars indicate means with standard error. Note that the intracranial fat body is significantly smaller in good performers compared with poor performers (*P = 0.016).

 
Most frequently there are mid-sized fat bodies positioned in the tentorium cerebelli (Figure 2Go). Regularly one can find fat bodies of different sizes between telencephalon, tectum, and cerebellum. From outside, the fat accumulations could only be observed when they were situated near the surface. Otherwise they were solely detected, and the extent of larger fat bodies between the 2 hemispheres was determined by studying the serial sections.

The allometric comparison of the brain and brain structure volume in relationship to the BW of all ducks is represented in Table 1Go. The CR individuals exhibit a significantly larger total brain volume in comparison with the pooled reference ducks (t = 2.823, df = 45, P = 0.007).


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  		Table 1. Volumes of brain structures (mm3) and allometric size indices in 4 breeds of domestic ducks1
 
For the comparison of the net brain volumes, volumes of the fat body and ventricular volumes were subtracted. As can be seen from Table 1Go, net brain volume of CR is significantly smaller in an allometric comparison with the reference breeds (t = –2.243, df = 45, P = 0.03). Also the cerebellar volume and the tegmental volume are relatively reduced in comparison to the reference group (t = –2.973, df = 45, P = 0.005; t = –2.565, df = 45, P = 0.014).

Among the 14 brain structures delineated, 10 were not reduced in CR compared with reference breeds. Next to the cerebellum and the tegmentum, the bulbus olfactorius and the hyperpallium apicale were significantly smaller (Table 1Go, Figure 6Go).


Figure 6
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  		Figure 6. Double logarithmic plots of brain structures vs. body weight. Individual data points, averages and standard deviations are given for 4 duck breeds. a) cerebellum, b) tegmentum, c) hyperpallium apicale, d) bulbus olfactorius. All structures show significant size decrease in Crested ducks.

 
After calculating a correlation analysis, an expected clear positive correlation between the fat body volume and the total brain volume was observed (r = 0.911, n = 21, P < 0.001). Correlations between the fat body and the reduced structures net brain (brain without fat), cerebellum, tegmentum, bulbus olfactorius, or hyperpallium apicale were not significant.

There was no strong correlation between increasing righting time of CR and any of the volumetric brain and fat body measurements.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
By analyzing the brain of CR in detail, we observed that the intracranial fat body has an impact on total brain volume and on net brain volume. The increased total brain volume is clearly associated with the fat body (positive correlation). If it is removed significantly smaller brains are found in CR. This is due to a reduction of several brain parts including cerebellum and olfactory bulb. An enlarged brain size due to an intracranial fat body in CR as well as the reduction of the cerebellum and the olfactory bulbs were also shown by Frahm et al. (2001). New in this study is the finding that apical hyperpallium and tegmentum are also relatively small in CR. This difference in results from the earlier paper might be explained by the larger sample of 21 CR and the fact that all individuals investigated in the present study had a crest in contrast to the sample by Frahm et al. (2001), which included 10 untypical individuals without a crest.

The olfactory bulb is strictly associated with olfaction, and the apical hyperpallium is a multimodal integration center that serves cognitive functions and is involved in part of the visual system. These brain parts should be discussed in other contexts, which are not major topics here. But the brain stem and cerebellar data are of interest.

The brain stem bears many structures that serve motor control for example descending motor pathways including vestibulospinal, reticulospinal, and rubrospinal fibers (for review see Nieuwenhuys et al., 1998), and the cerebellum can be regarded as a center of motor coordination (Ito, 1984). The cerebellum receives input from the reticular formation, the vestibular apparatus, proprioreceptors in muscles, joints, and skin as well as an input from lobe neurons of the lumbosacral part of the spinal cord that are associated with a special organ of equilibrium described by Necker (2006).

Unfortunately there are no simple correlations between fat body size and size of brain stem or cerebellum. Thus, we assume that these brain areas are part of a neuronal network that as a whole is suboptimally developed in those relatively small brains that exhibit a large fat body. This would be in line with the finding of small fat bodies but large cerebella in free-living ducks, which obviously have no problems in motor coordination (Frahm and Rehkämper, 2004).

The noncorrelation between righting time and fat body size is difficult to explain, particularly because there are differences between the 2 duck groups. Apparently the whole arrangement and interaction of brain structures and fat body are deciding for motor coordination so that it is difficult to receive a clear correlation. Perhaps a higher number of investigated animals and performed tests could disambiguate this.

But be that as it may, we would like to stress that the proposed test together with careful observations of the behavior in slightly challenged animals is able to filter those individuals out of a population that have functionally suboptimal brains and large intracranial fat bodies. Probably carriers of the undesirable defect but without obvious problems can also be selected by applying this test. None of these animals should be used for breeding. The mean righting times of normal ducks suggest that ducks used for breeding should require no more than approximately 1 to 2 s to right themselves. Thirteen tests per animal should be sufficient to differentiate reliably between affected and normal ducks.

The long history of breeding of CR and the associated problems (Requate, 1959) lead us to assume that heredity plays a key role. This is in agreement with Lancaster (1990). Thus the test might help to reduce the proportion of individuals with suboptimal brains and deficits in motor control from generation to generation, if only normal CR individuals are used for breeding. Because the test is easy to apply, every breeder can make use of it.


   ACKNOWLEDGMENTS
 
We would like to thank Inga Tiemann (Düsseldorf, Germany) for her support during the righting tests, Verena Ohms (Düsseldorf, Germany) for her support during the volume measures, and Claudia Stolze (Düsseldorf, Germany) for preparing the excellent serial sections. Thanks are due to Michael Mann (Omaha, Nebraska) for constructive discussion on the manuscript and for suggestions to improve the English. The support of the German Association of Poultry Breeders and the German Foundation for the support of Young Scientists in Poultry Research is kindly acknowledged as well.

Received for publication February 6, 2007. Accepted for publication May 24, 2007.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Bartels, T., J. Brinkmeier, S. Portmann, P. Wolf, M. E. Krautwald-Junghans, A. Boos, and N. Kummerfeld. 2001. Intrakraniale Fettkörper bei Hausenten (Anas platyrhynchos f. dom). Tierarztl. Prax. 29:384–390.[ISI]

Brinkmeier, J. 1999. Untersuchungen zur Inzidenz anatomisch-morphologischer Alterationen bei Hausenten (Anas platyrhynchos f.d.) mit Federhaube. Medical Veterinary Thesis. Tierärztliche Hochschule Hannover, Hannover, Germany.

Cnotka, J., H. D. Frahm, and G. Rehkämper. 2006. Intrakraniale Fettkörper und ihre potentiellen Auswirkungen auf Hirnbau und Verhalten bei haubentragenden Hausenten (3 Fallstudien). Dtsch. Tierärztl. Wschr. 113:27–31.

Frahm, H. D., J. Cnotka, and G. Rehkämper. 2005. Landente ohne Haube mit neurologischen Symptomen und ihr Hirnbau. Tierarztl. Umsch. 60:319–322.

Frahm, H. D., and G. Rehkämper. 1998. Allometric comparison of the brain and brain structures in the White Crested Polish Chicken with uncrested domestic chicken breeds. Brain Behav. Evol. 52:292–307.[ISI][Medline]

Frahm, H. D., and G. Rehkämper. 2004. Brain size, brain composition and intracranial fat bodies in a population of free-living crested ducks (‘Hochbrutflugenten’). Br. Poult. Sci. 45:590–597.[ISI][Medline]

Frahm, H. D., G. Rehkämper, and C. W. Werner. 2001. Brain alterations in crested versus non-crested breeds of domestic ducks (Anas platyrhynchos f.d.). Poult. Sci. 80:1249–1257.[Abstract/Free Full Text]

Ito, M. 1984. The Cerebellum and Neural Control. Raven, New York, NY.

Kamar, G. A. R., H. H. Hussain, L. Goher, and M. M. El Nadi. 1983. Lethal factors in Pekin Ducks. Egypt. J. Anim. Prod. 23:177–185.

Krautwald, F. 1910. Die Haube der Hühner und Enten. Diss. Med. Vet., Univ. Bern, Schweiz, Germany.

Lancaster, F. M 1990. Mutations and major variants in domestic ducks. Pages 381–394 in Poultry Breeding and Genetics. R. D. Crawford, ed. Elsevier, Amsterdam, the Netherlands.

Mpotsaris, A. 2006. Struktur und Anwendung eines Programms (NucleoScope) zur effizienten Volumenbestimmung in morphologischen Schnittpräparaten. Thesis. Univ. Düsseldorf, Fac. Med., Dusseldorf, Germany.

Mpotsaris, A., and G. Rehkämper. 2006. Automated morphometry: A new method of volume reconstruction from histological sections. J. Histotech. 29:192. (Abstr.)

Necker, R. 2006. Specializations in the lumbosacral vertebral canal and spinal cord of birds: Evidence of a function as a sense organ which is involved in the control of walking. J. Comp. Physiol. A 192:439–448.[ISI][Medline]

Nieuwenhuys, R., H. J. ten Donkelaar, and C. Nicholson. 1998. The central nervous system of vertebrates. Springer, Berlin, Germany.

Requate, H. 1959. Federhauben bei Vögeln. Eine genetische und entwicklungsphysiologische Studie zum Problem der Parallelbildungen. Z. Wiss. Zool. 162:191–313.

Stephan, H., G. Baron, and H. D. Frahm. 1988. Comparative size of brains and brain components. Pages 1–38 in Comparative Primate Biology. H. D. Steklis and J. Erwin, ed. Alan R. Liss, New York, NY.





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